1. Field of the Invention
The present invention relates to an image inputting apparatus which changes a reading capability in correspondence to a character to be recognized and inputs an original image.
2. Related Background Art
Generally, an image reading apparatus such as an image scanner often uses what is called a (1 : 1/2) optical system in which an original put on an original base glass is scanned by a light source and a mirror and is exposed onto an image sensor or a photo sensitive material.
As shown in FIG. 9, according to the (1 : 1/2) optical system, an original P on a fixed original base glass 100 is illuminated by a light source 101 and an image light reflected by mirrors 102, 103, and 104 is formed as an image onto an image sensor 106 or the like through an image forming lens 105. A mirror unit 108 in which the mirrors 103 and 104 are installed is scanned at a speed of 1/2 of a scan speed of a lamp unit 107 in which the light source 101 and the mirror 102 are installed, thereby setting an optical path length from the original surface to the image forming lens to be always constant. The mirror unit is scanned in the direction (sub-scan direction) perpendicular to the longitudinal direction of the image sensor. A scan amount of one line is set so as to be equal to a reading width in the longitudinal direction (main scan direction) of the image sensor pixel.
In many cases, the image scanner constructed as mentioned above is used as a device for a computer input.
There is an OCR function as one of the main applications of the image scanner. The most significant factor of the OCR is a recognition ratio (ratio of the number of characters which could accurately be recognized to the number of characters which have been read). The recognition ratio largely depends on a reading performance (resolution) of the image scanner.
To measure the recognition ratio, there is a case of using a chart on which alphabetic characters "e" are written on the whole surface as shown in FIG. 10. Whether the alphabetic characters "e" can accurately be recognized or not depends on whether a thin lateral line in the central portion of each character can be read or not . FIG. 11 shows an output of the image sensor in the case where the lateral line of the alphabetic character "e" has been read. It will be understood from the diagram that since the output value approaches the threshold level as the line of the character becomes thin, a possibility such that the character line after completion of the binarization is determined to be white increases. Thus, the image data of the alphabetic character "e" in which the lateral line in the central portion has been cut out is sent to the OCR and an erroneous recognition is caused.